We like to talk about contemporary art being edgy and risky, but there are risks and risks. In Britain Damien Hirst or Tracey Emin might get a bad review; last year Ai Weiwei, China’s most famous living artist, was almost killed.

He was in Chengdu, capital of Sichuan province, on August 12 2009. At three o’clock in the morning police kicked in his hotel bedroom door. He asked them for identification; in response he was punched hard on the side of the head.

“I didn’t take it seriously,” he told me, but a month later, while he was installing an exhibition in Munich, he suffered a cerebral haemorrhage as a result of this blow. “Luckily I had a doctor in Munich who operated on my head and released the pressure. Now I’m fine again.”

At 53, Ai Weiwei is an increasingly prominent figure in the international art world, his work a mixture of the in-your-face outrageousness familiar from recent Western art, a sense of traditional Chinese techniques and the sort of political courage one associates with the Eastern European dissidents of the Eighties.

He collaborated with the Swiss architects Herzog and de Meuron as artistic adviser on the design for the Bird's Nest Olympic Stadium – one of the most strikingly successful buildings in modern China. Now he is in London working on his contribution to the Unilever Series in the Turbine Hall of Tate Modern, opening next Tuesday .

A burly panda of a man, he speaks quietly and thoughtfully, even when he is describing his near-death experience. This meditative manner, however, is belied by his actions. In his native China, Ai Weiwei has been an increasingly vociferous critic of the Communist government. For example, having helped to design the Bird’s Nest Stadium, he then refused to have anything to do with the opening of the Olympics.

“When I saw that the celebrations were going to become party propaganda, I just told them I wasn’t going to be part of it. I think the ceremony betrayed the idea of having the Olympics in China – having a more open society with a spirit of freedom. But I’m very pleased with the architectural outcome.”

It was his dissidence that led to the confrontation in Chengdu. In 2008 there was a catastrophic earthquake in Sichuan, in which a large number of children were killed when their schools collapsed.

“We asked the government just to tell us who was dead. They said, 'No, no, no, this is a top national secret. We’re not going to give out the names.’ So I said, forget about it. I’ll make my own investigations through the internet. And we organised hundreds of volunteers and sent some of them to Sichuan to go round door to door asking the parents.”

After a year, he and his collaborators had a list of over 5,000 students aged between three and 19 who had died in the earthquake, together with their date of birth and which school they were in. There have been persistent allegations that the schools fell down because they had been badly built as a result of corruption and lack of proper supervision. The list seemed to confirm those suspicions – all the children had attended around 20 schools that had disintegrated into dust.

As part of his exhibition in Munich, Ai Weiwei covered the front of the Haus der Kunst with thousands of brightly coloured school back-packs. Together these spelled out in Chinese characters a quotation from an interview with the mother of a dead child: “She lived happily for seven years in this world.”

Ai Weiwei published the information about the dead schoolchildren on his blog, for which he claimed a readership of 12‑13 million. “That really made the government very nervous. So they shut down my blog one day. Then they tried to threaten me, they had me tailed, tapped my phone, had my bank account checked – all those things.”

He was in Chengdu to testify at the trial of a fellow earthquake activist when he had that almost fatal run-in with the local police.

Ai Weiwei is no stranger to the consequences of political opposition in China. In fact, he grew up with them. His father, Ai Qing (1910-96), was one of the most highly regarded of 20th-century Chinese poets. In 1967, at the start of the Cultural Revolution, he was exiled to a remote village; his family, including the 10-year-old Weiwei, accompanied him.

“My father was punished by being made to clean the public toilet for five years. I grew up in those conditions. He was criticised and beaten and kept in very severe physical deprivation – the worst conditions of life you can imagine. It couldn’t be any worse, or you’d just die. He never had a single day of holiday, because people never stopped using the toilets.”

After the death of Chairman Mao in 1976, the family returned to Beijing, where Weiwei studied at the Film Academy. In his third year, his then girlfriend got permission to study in America and he decided to go, too.

“I remember my plane circling New York before landing, with the lights below like jewellery, so much energy. It completely destroyed the education I had had about capitalism. I began to think of this as a place of excitement.”

He stayed in the US for 12 years, encountering Duchamp, Dada, Surrealism, and conceptual art – all of which had a strong influence on his later work.

He thought he would never go back to China. Then – because his father was ailing – in 1993 he did.

“Everybody said it had changed a lot, but because I was already used to life in New York, I was more conscious that some things never changed. The system is still a very strict Communist system which still – today – doesn’t allow freedom of speech, free access to information or freedom of association. And those things are what I value the most. I don’t care about a few more buildings, or a lot of expensive cars.”